A new Dutch study on mobile phone signals finds that using a cell phone in restricted areas, such as hospitals, can be dangerous. In the study, published Wednesday in the online journal Critical Care, researchers measured the impact of electromagnetic interference (EMI) from cell phone use on hospital equipment such as ventilators and pacemakers. Signals that were equal in strength to those given off by second- and third-generation mobile phones significantly interfered with medical devices, and the study's authors categorized 75% of those incidents as "hazardous," meaning that the interference had a direct impact on patient health, or "significant," indicating that it distracted health care providers. Hazardous incidents included the sudden switching off or restarting of machines  which could mean disruption of a patient's feeding tube, ventilator, pacemaker or dialysis machine  and most events occurred when mobile phones were within 3 cm of critical-care equipment.

Dr. Erik van Lieshout, a critical-care physician at the University of Amsterdam's Academic Medical Center, and his team were prompted to begin their study last year, when they wanted to use 3G mobile phone technology to monitor mobile intensive care units remotely. They asked a Dutch telecom company if it would be safe to use UTMS, or Universal Mobile Telecommunications System, technology  which, like W-CDMA in the U.S., facilitates data transfer  near medical devices. The company didn't know. So van Lieshout and his colleagues decided to evaluate the impact of cell signals themselves; they tested the signals' effect on 61 medical devices and found that 26 (or 43%) were disrupted by EMI. Most incidents were caused by a GPRS (General Packet Radio Service) signal, a mobile data service that handles heavy-duty data transfer in international GSM networks, used by companies such as Cingular/AT&T and T-Mobile.

First-generation cell phones handled only voice data, but subsequent generations have tacked on technology that allows data transmission, which uses more electricity than older phones  it's that extra juice that researchers think interferes with medical devices. Though cell phone technology differs in the U.S., Europe and Asia, the study's authors say that, in general, 10% of medical devices experience interference from second-generation mobile phones, and that while critical incidents are rare they are "potentially lethal and...are not recognized as such."

In their research, van Lieshout and colleagues generated maximum mobile phone power signals with a signal generator, rather than with actual phones, in order to achieve results that could be replicated in other studies. Mobile phones use more power in low-coverage areas or when they're far from a cell tower; with greater coverage and close proximity to a tower, phones use less power. "It's possible that in many hospitals there is low coverage because of the concrete in the building, and it's possible that your mobile phone is transmitting like hell to get in contact with the base station," says van Lieshout. His research team proposes the one-meter rule, which recommends that mobile phones be used more than three feet from medical equipment  or not at all in patient areas, if possible.

All hospitals have restrictions on where mobiles can be used. In the U.S., those guidelines are recommended by the Food and Drug Administration and the Center for Devices and Radiological Health. But van Lieshout says the reality is that "some doctors violate the rules, and there's an increase in the use of cell phones so it's hard to control." Rick Wade, senior vice president of the American Hospital Association, says that hospitals follow recommendations but set their own policies. He agrees that the official rules "don't deter anybody. Three feet is not an enormous amount of space," he says.

That's why van Lieshout wants hospital equipment, such as ventilators and monitors, to be tested and certified as mobile-phone proof. "It's not up to the hospital to test all the equipment," he says, "it should be done by the company."

Another solution might be to minimize the power output of mobile phones altogether by adding an antenna to the hospital to boost internal signal strength, a system that CellAntenna Corp. has installed in several U.S. hospitals. "The barrier to that for hospitals would be cost," says Wade. "Hospitals are investing a lot and my sense is that cell phone towers would not be at the top of the list."

But the question is, given all the variability in signal strength and cell phone use outside the laboratory, do phones pose a real-world threat? Not really, according to a study published in March in Mayo Clinic Proceedings, which found that "normal" cell phone use did not interact with medical devices. That study has a Mayo Clinic committee rethinking the clinic's current mobile phone policy, which is to ban phones from areas in which invasive procedures are being done, according to Jeffrey Tri, an electrical engineer and an author of the study. Tri says that the Dutch study used a signal strength of two watts, which, to his knowledge, is at least three times more power than any U.S. cell phone would emit. According to Tri, U.S. cell phones usually fall below the 600-milliwatt output level, and some are even capped at 250 milliwatts. "We think the value of [cell phone] technology really outweighs the disadvantages and we really couldn't find causes of concern to not change the policy," says Tri. "Our goal is to allow cell phone use everywhere but in pediatric and neonatal intensive care units and surgery because we have not done testing in those areas."

More studies need to be done on the effects of mobile phone use on medical equipment. In the meantime, if not for the sake of technical interference, think about the other reasons people don't yap away on their mobiles in critical areas. "We've all been around people who use cell phones," says Wade. "There is a line you draw  and you have to."